Bent end electric lamp



May 5, 1970 I v. N. lAClAN Cl ETA!- 3,510,719

I v BENT ,END ELECTRIC LAMP Filed June 14, 1968 Inventors: ViCtOT" N. Iacianci Victor- A.l evand,d1i

b9 fla f;

Their Att 1-Way United States Patent O 3,510,719 BENT END ELECTRIC LAMP Victor N. Iacianci, Cleveland, and Victor A. Levand, Jr.,

Lyndhurst, Ohio, assignors to General Electric Company, a corporation of New York Filed June 14, 1968, Ser. No. 737,052 Int. Cl. H01j 5/46 US. Cl. 313-333 4 Claims ABSTRACT OF THE DISCLOSURE In an incandescent lamp comprising an elongated tubular envelope of vitreous material having sharply bent ends with hermetic seals at the extremities of the bent ends and with compressed pinch portions at the areas of the bends, the current supply conductors extending from the exterior through the hermetic seals, through the bent ends and through the bends to the respective ends of a coiled filament extending longitudinally of the main body portion of the envelope, the portion of each current supply conductor which extends through a bend is composed of a flexible helical coil of wire which is substantially thicker than the wire of the filament and which has its surface embedded in the compressed pinch portion at the bend.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to electric lamps, and more particularly to elongated tubular double-ended incandescent lamps having laterally extending end portions. Still more particularly, the invention relates to an improvement in the construction of current supply or leadin conductors for such bent end lamps.

Description of the prior art There is described and claimed in Pat. 3,080,497 to E. B. Noel and V. A. Levand, a lamp of bent end type comprising an elongated tubular envelope having laterally extending end portions which are joined to the main body portion by flattened or compressed bend portions and which have their extremities hermetically sealed. Lead-in conductors extend through said hermetically sealed extremities, through the bent end portions and through the bends to respective ends of a filament which extends longitudinally of the main body portion of the envelope. In this way, the hermetic seals are removed from the vicinity of the hot main body portion to avoid oxidation of the lead in wires.

Some ditficulties were experienced in the way of failure of some of the lamps early in life. In accordance with Pat. 3,237,045 to I B. Volzer and L. Wenig, it was discovered that failure of the lamps due to cracks developing in the bend portion of the envelope or to breakage of a thin foil seal portion of the lead-in conductor was caused by strains introduced into the lead wires and into the bend portions of the enyelope during manufacture of the lamp. In accordance with that patent the lead-in wire was permitted to yield, upon cooling and contracting, by virtue of an expansion bend in the portion of the lead wire located in each of the laterally extending legs of the envelope. While that construction did further reduce the number of lamp failures, it did not entirely eliminate the problem.

SUMMARY OF THE INVENTION It is an object of the present invention to still further reduce, or even virtually eliminate, the problem of lamp failure due to cracks at the bends. Apparently, the fused silica or quartz at the bend tends to wet the molyb- 3,510,719 Patented May 5, 1970 denum lead wire and adhere so tightly as to cause shaling or cracking when the lead wire shrinks away from the quartz, despite the presence of the expansion bend in each leg portion of the lamp.

In accordance with the present invention the problem is solved by forming that portion of each lead-in conductor which extends through a respective bend as a flexible member, preferably as a helical wire coil which has relatively small portions of its surface embedded in the quartz at the bend.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS The lamp shown in the drawing and specifically described herein for purposes of illustration, is a quartz infrared lamp of the type shown in the aforesaid Pats. 3,080,497 to Noel et al. and 3,237,045 to Volzer et al. The lamp comprises a tubular quartz envelope 1 having a main body portion 2 with bent end portions 3 extending laterally thereof and joined thereto by compressed bend portions 4. The main body portion 2 contains a helically coiled tungsten wire filament 5 which is supported in the envelope axis by spaced supports such as discs 6. The filament 5 is connected at each end to a lead-in conductor 7 which extends through an associated bend portion 4 and end portion 3 of the envelope to the exterior thereof and which is made up of several parts preferably composed of refractory metals such as tungsten or molybdenum. A seal portion 8 at the extremity of the bent end 3 is compressed upon and hermetically sealed to a thin molybdenum foil portion 9 of the lead-in conductor 7.

In accordance with the present invention, the portion of the lead-in conductor 7 which extends through a bend 4 is a flexible member, more particularly a helical coil 10 which is preferably of tungsten wire which is substantially thicker than the wire of the filament S and which is therefore not heated to incandescence by passage of the current therethrough, as is the filament 5. In the form shown in FIGS. 1 to 4, the lead-in conductor also includes an outer lead portion 11 which may be of molybdenum and is attached to one end of the foil 9; an inner lead portion 12, preferably also of molybdenum and which is connected at one end to foil 9 and has its other end fitted tightly in the interior of a few turns of the connecting coil 10; and a spud 13, preferably also of molybdenum, and which has one end fitted tightly in a few turns of the other end of the connecting coil 10, the other end of spud 13 being fitted securely into a few turns of the filament. The inside diameter of filament coil 5 is somewhat larger than that of the connecting coil 10, and therefore the spud 13 is preferably provided with a flattened spade end 14 which securely engages the filament turns and which may be of the shape more fully described and claimed in Pat. 2,830,217 to W. F. Hodge.

In a preferred method of manufacturing the lamp, it is assembled as a straight unit as illustrated in FIG. 4, preferably by one of the methods disclosed in either Pat. 2,900,771 to Levand, or 2,855,265 to Foote et al. The result is a straight length of quartz tubing containing a filling of inert gas such as argon at a pressure of several hundred torr and having its ends hermetically sealed at 8 around portions of the lead-in conductors 7 to which is attached the filament which has been stretched slightly prior to completion of the seals 8. Thereafter the envelope 1 is locally heated at an area 4 by intense flat flames from opposed burners to soften and collapse it upon opposite sides of the surface of a portion of a connecting coil 10, after which the softened envelope portion 4' is bent, together with the enclosed portion of the coil 10, to form a bend 4. The same procedure is followed to form the second bend 4 at the other end of the envelope.

As shown in FIGS. 2 and 3, the surface at the inner and outer sides of the bent portion of the coil 10 is slightly embedded in the quartz. In this case, the coil 10 is preferably wound with its adjacent turns touching each other. The flexibility of the coil 10 in the bend 4 permits it to contract upon cooling after the bend forming operation has been completed, without stressing the quartz in the bend so as to form cracks. During normal lamp operation neither the quartz nor the coil in the bend 4 is heated to any temperature approaching that required to soften the quartz for the bending operation, and the flexible coil 10 therefore effectively avoids any problems of introducing destructive strains into the quartz during subsequent use of the lamp.

In the modification shown in FIG. 5, parts corresponding to those in FIGS. 1 to 4 are numbered the same with the addition of the letter a. As shown in FIG. 5, the connecting coil 10a is wound to a pitch such that it can be connected in intermeshing screw thread engagement with the filament coil 5a. In this case, the filament coil 5a extends completely through and a short distance beyond the end of the connecting coil 10a, into the envelope leg 3a where it is firmly connected to the inner lead wire 12a. In this particular case, the diameter of the Wire in coil 10a is slightly more than twice the diameter of the wire in filament coil 5a, and the coil diameter, as measured between the centers of the wire, is approximately the same for both coil 10a and filament coil 5a. Therefore, the inside diameter of coil 10a is less than the inside diameter of filament coil 5a, and the outside diameter of coil 10a is greater than the outside diameter of filament coil 5a. Consequently, the lead wire 12a, which would fit tightly inside coil 10a, must be provided with a flattened spade end 16 in order to securely engage the end of filament coil 5a which projects beyond the coil 10a.

In the modification shown in FIG. 6, parts corresponding to those in FIGS. 1 to 4 are numbered the same with the addition of the letter b. This modification is like that shown in FIG. 5 in that the coils 10b and 5b are in screw thread engagement. The filament coil 5b may extend all the way through coil 10b and terminate at the end thereof in the envelope leg 3b. In this case, as in FIG. 2, the lead wire 12b fits snugly and firmly in the inside of the coil 10b.

What we claim and desire to secure by Letters Patent of the United States is:

1. A double-ended elongated electric incandescent lamp comprising a sealed gas-filled tubular envelope of vitreous material having sharply bent ends extending laterally a substantial distance from a main body portion with hermetic seals at the extremities of respective said bent ends and with compressed pinch portions at the areas of respective bends; an incandescible helically coiled filament having an effective length extending longitudinally of the main body portion of said envelope; elongated non-incandescible current supply conductors extending from the exterior at each end of the envelope through the hermetic seal thereat, through the respective bent ends and through the respective bends to the respective ends of the eflfective length of the filament. coil; the portion of each current supply conductor which extends through a bend being a flexible helical coil of wire substantially thicker than the filament wire and having portions of its surface embedded in the compressed pinch portion at the area of the bend.

2. A lamp as set forth in claim 1 wherein the envelope is composed of essentially fused silica and the parts of each of said current supply conductors are composed of refractory metal of the group consisting of molybdenum and tungsten.

3. A lamp as set forth in claim 1 wherein adjacent end portions of a flexible helical coil portion of a current supply conductor and of the filament coil are interconnected by a wire spud fitted tightly in the interior of respective said coils.

4. A lamp as set forth in claim 1 wherein the flexible helical coil portions of the current supply conductors have the same pitch as the filament coil and the ends of the filament coil are in screw thread inter-engagement with the respective flexible helical coil portions.

References Cited UNITED STATES PATENTS 3,237,045 2/1966 Volzer et al. 313279 RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 3 l3279 

